While I can understand the mechanism of selection, I find it difficult to
understand what drives neutral drift. I'd appreciate it if you would explain
it. It seems to me to be a radical departure from natural selection. What is
the significance of their "faster accumulation in the genome" that you
mention?

Bob: >But to do so would introduce a problem that the statement probably

>wanted to avoid, namely, that the only direct evidence we have that

>natural selection is the causal factor in DMW is bacterial resistance

>to antibiotics, and what Gould called "short-term evolution" (STE)

>studies, such as the finch's beak, peppered moths, spotted guppies,

>and so forth. These studies are the only basis for the claim that

>natural selection is the causal factor for all changes we see in the

>fossil record and the tree of life. The operation of natural selection

>throughout the entire tree of life is an extrapolation from such studies.

>Or to say it differently, evolutionary biologists hold that socalled

>macroevolution, or large innovative changes in DWM is microevolution

>WRIT LARGE. This claim, however, is not a fact. Thus while DWM itself

>is factual, its mechanism is not.

Tim: <<Descent with modification can arise from multiple mechanisms, some are

selective, others are not. I do agree that in most cases, it is a practical

impossibility to determine what specific factors played a role at specific

times.>>

Bob: >To continue, such an extrapolation is unwarranted because of the simple

>fact that changes observed in STE studies and bacterial resistance are

>_reversible_. While finch's beaks become more robust in times of drought

>when seeds have tougher shells, they revert to the more slender shape when

>climate returns to normal and seed shells less hard to crack. Such

>reversibility disqualifies STE from serving as the mechanism of DWM, or

>at least raises serious questions about it. The statement would be more

>forthright and therefore improved if it acknowledged this.>

Tim: <<Reversibility is irrelevant and in fact, many of the changes are not

reversible at the genetic level. Remember that there is a gaping chasm

between genotype and phenotype. The mapping between the two domains is

anything but linear in all but the rarest situations. Point mutations

can confer antibiotic resistance. However, given the odds of hitting that

exact site again to exactly reverse the point mutation, it's more likely

that a mutation that eliminates resistance will occur in another

portion of the genome. Thus a phenotypic reversal (short-term or otherwise)

does not equate to a genomic "reversal". And we have a recently described

case where a bacterium acquired streptomycin resistance in a "long-term"

manner such that loss of the resistance, even in the absence of the

antibiotic, was selected against (A secondary mutation occurred which

effectively "locked in" the first one). So, we can say that ratchet-like

evolutionary progression has been observed even over short timescales.>>

One case doth not a theory make. Moreover this is not a ratchet-like
evolutionary progression, as you claim. It is step one. Has anything been
observed that builds on step one to produce step two? Unless it has you do
not have a progression. You have merely a locked-in bacterium

I suspect you are overstating your case. Does your "bacterium [that]
acquired streptomycin resistance" that you mentioned earlier have
"mind-bogglingly huge morphology- or genetic-space available to it"? I doubt
it. If so, tell mme what it is.

Bob: >Finally, DWM has produced the enormous diversity of life forms in the

>tree of life. This is acknowledged briefly in the statement. Natural

>selection is ideally suited to produce diversity.>

Tim: <<Actually, neutral drift also contributes to the production of
diversity.>>

Bob: >But what is more difficult to explain is _disparity_, or the highly

>consideration at least acknowledge that existence of the hierarchical

>organization and discontinuities in nature, instead of silently passing

>by on the other side of the road?>

Tim; <<Nobody is failing to acknowledge the hierarchical pattern of life and

discontinuities. These are what led to the conclusion of descent with

modification in the first place.>>

Your first sentence in the above paragraph is simply not true. Read the
statement that Dick Fischer presented and see if you can find hierarchical
organization and discontinuities in it. Moreover, evolution abhors a
discontinuity. Many evolutionary biologists are busy trying to iron them out.

Tim: <<Discontinuity is a product of speciation (a mechanism of evolution)
and

extinction.>>

Show me.

Tim: <<Such discontinuities tend to manifest more in the

morphological arena than the biochemical one. Also, hierarchical

organization is a manifestation of the rates of change and the nature

of speciation and organismal genetics. Understanding the timing and details

of specific steps behind evolution is real challenge, IMHO.>>

Although these words may make sense to you, they don't to me.

I think our brief discussion illustrates my point that the statement
presented by Dick is incomplete, and I add, even misleading. It suggests
that evolutionary theory is a done deal. I continue to hold that descent
with modification needs a robustly supported mechanism (which in my view it
doesn't have) and in addition, an unambiguous refutation of intelligent
design, to substantiate its claim to be the all encompassing theory it wants
to be.